1. Field of the Invention
The invention relates to a technology for determining whether there is an abnormality in a tire/wheel assembly in a vehicle. More particularly, the invention relates to a technology for enhancing accuracy of the determination.
2. Description of the Related Art
There is a known technology for detecting a state of a tire/wheel assembly in a vehicle provided with the tire/wheel assembly which is constituted by fixing a tire, that is filled with compressed air, to a wheel, while the vehicle is running (for example, Japanese Patent Laid-Open Publication No. 08-132831).
More particularly, Japanese Patent Laid-Open Publication No. 08-132831 discloses a technology for extracting a uniformity component of the tire based on a wheel speed signal indicative of a wheel speed, which is a rotational speed of the tire/wheel assembly, and for detecting a state of the tire/wheel assembly, including a standing wave of the tire, and wear of the tire, based on the extracted component.
According to the technology disclosed in Japanese Patent Laid-Open Publication No. 08-132831, the state of the tire/wheel assembly is detected with reference to the wheel speed signal. However, for example, a state of an air pressure in the tire, as an example of the state of the tire/wheel assembly, is attempted to be detected, the accuracy of detection of the air pressure in the tire may deteriorate when the wheel speed fluctuates, for example, when the vehicle accelerates/decelerates, or when the vehicle is running on a rough road. This is because a component which does not accurately reflect the air pressure in the tire, that is, noise (disturbance) for the air pressure detection, is easily mixed in the wheel speed signal.